Our understanding of fathering has lagged far behind our understanding of mothering, yet fathers have a substantial impact on the well-being of their offspring. The overall objective of this application is to understand the behavioral, molecular and epigenetic mechanisms that contribute to the effects of fathering on offspring. The central hypothesis is that fathering, like mothering, has long-lasting, transgenerational consequences for offspring behavior that are mediated via epigenetic changes in the genome that influence brain gene expression. The rationale that underlies the proposed research is that studying natural variation in social behavior in a tractable vertebrate system with sophisticated paternal behaviors is likely to have success identifying the causes and consequences of fathering in other organisms, including humans. There are two specific aims: 1: Identify the sensitive period and the molecular mechanisms underlying the effect of fathering on offspring. The working hypothesis for this aim is that fathering influences offspring gene expression during a sensitive period in development that has consequences for offspring behavior later in life. 2: Identify the epigenetic modifications caused by fathering. The working hypothesis for this aim is that fathering causes epigenetic modifications to the genome that influence offspring brain gene expression, behavior and stress physiology. The expected outcome of this project is a detailed understanding of the basic mechanisms by which family environments created by different fathering styles exert protective effects on offspring. These outcomes are expected to have an important positive impact because understanding the impacts of fathers on offspring could enhance the development of interventions that promote the adoption of healthy behaviors. The contribution of the proposed research is expected to be a detailed understanding of the behavioral, molecular and epigenetic mechanisms by which fathers influence their offspring using a new model system for fathering. This contribution will be significant because it will reveal if fathering, like mothering, can influence subsequent generations via epigenetic modifications to the genome. The proposed research is innovative because it utilizes a new genomically-enabled model organism in which fathers are the sole providers of parental care (threespined stickleback fish). The benefit of using a system with sole paternal care such as sticklebacks is that we can isolate the effects of fathering from the effects of mothering.